If the Ka of a monoprotic weak acid is 3 8 10 6, what is thepH of a 0...

If the Ka of a monoprotic weak acid is 3.8 Ã— 10-6, what is the pH...

4.4 Ratings (714 Votes)

costruct the ICE table

no need to cinsider H2O concentration since it is very large

Â Â Â Â Â Â Â Â Â Â Â HA +Â Â Â Â Â Â Â Â H2OÂ Â Â Â Â Â <----->Â Â Â Â Â H3O+ + A-

IÂ Â Â Â Â Â Â Â Â Â Â 0.11Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 0Â Â Â Â Â Â Â Â Â Â Â Â Â 0

CÂ Â Â Â Â Â Â Â Â Â -xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â +xÂ Â Â Â Â Â Â Â Â Â Â +x

EÂ Â Â Â Â Â Â Â Â Â Â 0.11-xÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â +xÂ Â Â Â Â Â Â Â Â Â Â Â Â +x

write the disociation expression

Ka = [H3O+][A-] / [HA]

3.8 Ã— 10^-6 = [x] [x] / [0.11-x]

3.8 Ã— 10^-6 = x² / [0.11-x]

x² + 3.8 Ã— 10^-6x - 0.418 * 10^-6 = 0

solve the quadratic equation

x = 0.000644 = [H3O+]

pH = -log[H3O+]

= -log [0.000644]

= 3.19

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